Regulations for certifying a helicopter require the anti-torque tail rotor to be protected so as to avoid said tail rotor impacting against the ground when the helicopter takes a nose-up position close to the ground.
For example, when landing in autorotation, the pilot makes the helicopter take a nose-up position close to the ground, a procedure known as “flaring”. Consequently, there is a risk of the tail rotor coming into contact with the ground, and that could lead to a catastrophic situation.
Furthermore, when landing at high speed, the pilot causes the helicopter to take a nose-up position in order to brake it.
Thus, aircraft, and in particular helicopters, advantageously include protection against impact with the ground in the event of the aircraft taking a strongly nose-up position.
For example, a crushable and replaceable tail bumper is known that is arranged in a structural element. For example, the Applicant's helicopter known under the trademark Gazelle® is provided with such a bumper inside the keel of its faired tail rotor, i.e. inside the bottom structural element of said faired tail rotor that faces the ground when the helicopter is standing thereon.
Such a bumper nevertheless needs to be changed or repaired after each occasion it comes into contact with the ground. The repairs are sometimes performed by the owner of the rotorcraft and thus under conditions that are not as good as they might be.
Alternatively, other rotorcraft are provided with a resilient skid having a single blade.
A first end of the skid is provided with a curved portion, while its second end is fastened by two distinct fastener means to the structural element for protection. Document FR 2 554 210 describes a skid of that type arranged under the tail boom of a helicopter.
The skid is thus cantilevered-out, which explains why the term “cantilever” is sometimes also used to designate such a skid.
Although effective, it should be observed that the cantilever of such a skid gives rise to high levels of force at the fastener means between the skid and the structural element. The structural element therefore needs to be dimensioned accordingly so as to be capable of withstanding the forces generated by the skid on coming into contact with the ground, with this being achieved by using local reinforcement, where such reinforcement is harmful to the overall weight of the rotorcraft and also constitutes extra expense.
Furthermore, the skid sometimes leads to a disagreeable bounce effect that tends to push the structural element away from the ground.
In addition, it has been observed that such a skid has sometimes given rise to incidents on certain aircraft.
Starting from a given nose-up angle, the angle between the skid and the ground as formed by the curved portion can cause the skid to become jammed and consequently leads to the structural element being dented where it is fastened to the skid. Furthermore, certain occasions of losing control of a rotorcraft have been caused by the skid catching on the ground (net, vegetation, etc. . . . ).
Furthermore, certain touchdowns can lead to the structural integrity of the tail boom being put at risk. As a result significant maintenance action should be expected. In order to remedy such incidents, various solutions may be provided, such as, for example:                accepting plastic deformation of the skid during an impact; or indeed        hinging the skid to the structural element for protection, and arranging an oleo-strut between the skid and the structural element.        
Finally, skids are difficult to develop. Thus, skids need to be sufficiently stiff for the pilot to be aware that contact has occurred between the skid and the ground, while also being sufficiently flexible to absorb the energy that results from such contact without generating excessive forces in the structure.
Other damper devices have also been envisaged in the following additional documents.
For example, additional document FR 362 365 relates to a car suspension and cannot seriously be considered for protecting a helicopter tail rotor. Document FR 362 365 describes a buffer provided with an elastomer having a recess formed therein to constitute an air chamber, with orifices enabling the air chamber to communicate with an outside medium.
Similarly, additional document FR 2 873 641 relates to a device that is applicable to car doors, the device having a deformable shell extending between two panels of a door.
Additional document U.S. Pat. No. 5,445,430 relates to an armrest having a shell that is closed in part by a membrane that is suitable for rupturing in the event of an impact.
Additional document WO 2008/054401 describes an anti-crash device having an airbag that is inflatable by two distinct sources of gas and that is provided with venting valves.
Finally, additional document U.S. Pat. No. 4,399,963 relates to a skid wheel for light aircraft that is inserted in a body made of an elastic material.
It can be understood that those additional documents relate to subjects that are far removed from the restricted technical field of the invention.